1. Field of the Invention
The present invention relates to a colorimetric apparatus and colorimetric method capable of colorimetry.
2. Description of the Related Art
Applying a fluorescent brightener to a sheet (printing medium) such as printing paper in order to improve the brightness is known. The fluorescent brightener has a characteristic of emitting light in the visible light wavelength range upon receiving irradiation of light outside visible light wavelengths, typified by ultraviolet rays. Thus, the color reproduction of an image output from a printing apparatus changes depending on an observation light source. In a printing apparatus using a sheet containing a fluorescent brightener, colorimetry is sometimes performed by measuring the spectral radiance factor of light generated by the fluorescent brightener, in order to faithfully estimate the reproduction color of an output image under an arbitrary observation light source.
A total spectral radiance factor representing the color of a sample under an arbitrary observation light source is obtained by compositing a reflection spectral radiance factor containing no fluorescence of the sample and a fluorescence spectral radiance factor serving as a fluorescent component. To acquire the total spectral radiance factor of a sample, it is necessary to acquire two spectral radiance factors respectively describing the reflection spectral radiance factor containing no fluorescent component of the sample, and the fluorescence spectral radiance factor serving as the fluorescent component.
In general, to acquire these two spectral radiance factors, a sample is irradiated with two or more types of light sources including a white light source having wavelengths in the visible light range and an ultraviolet light source having wavelengths in the ultraviolet light range, and the spectral radiance factor of the sample is detected using a spectral radiance meter for each light source. Japanese Patent Laid-Open No. 08-313349 discloses a method of measuring spectral radiance factors of a sample under two types of light sources, that is, a light source containing ultraviolet light and a light source containing no ultraviolet light, multiplying the measured spectral wavelengths by load coefficients, and compositing them, thereby obtaining the total spectral radiance factor of the sample.
In the sheet colorimetric method disclosed in Japanese Patent Laid-Open No. 08-313349, measurement needs to be executed while switching the plurality of types of light sources regardless of whether or not the sheet contains a fluorescent brightener. For a sheet containing no fluorescent brightener, no spectral radiance factor need be measured under the ultraviolet light source essentially, and this measurement generates an unwanted measurement time.